CO2 efficient burying and reinjection system and method based on liquid phase injection

Abstract

The invention discloses a CO2 efficient burying and reinjection system and method based on liquid phase injection, and belongs to the technical field of liquid phase CO2 reinjection. The system comprises a pipe tank precooling system, a first-stage injection pipeline supercooling system, a pipeline overpressure bypass pressure relief system, a pressurizing medium backflow pressure supplementing system and an underground plug removal injection system. The problems that a first-stage injection pipeline is vaporized, overpressure is directly released after stopping transportation, the pressure of a storage tank is too low in the middle and later periods of reinjection, and underground blockage is caused during reinjection can be effectively relieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of liquid phase CO2 reinjection, and in particular relates to a CO2 efficient storage and reinjection system and method based on liquid phase injection. Background Art

[0002] Carbon dioxide storage is an effective way to achieve carbon emission reduction. Its basic concept is to capture and pressurize carbon dioxide, then inject it into the reinjection well through the reinjection pipeline and store it in depleted oil and gas reservoirs or saline water layers. The critical temperature of a relatively pure carbon dioxide medium is about 31.1℃ and the critical pressure is about 7.38MPa. Carbon dioxide used for reinjection and storage generally also contains impurities such as nitrogen and hydrogen sulfide, which affect the critical pressure and critical temperature.

[0003] Carbon dioxide reinjection can be used for oilfield recovery (EOR) or geological storage, and can be achieved through long-distance pipeline transportation followed by wellhead reinjection and wellhead storage followed by liquid phase reinjection. Compared with oilfield recovery, geological storage has relatively low injection temperature requirements, which provides an opportunity to implement efficient and energy-saving injection, that is, to fully utilize the advantage of the relatively large density of low-temperature CO2 and reduce the reinjection pressure as much as possible through the contribution of wellbore hydrostatic pressure; further, compared with long-distance pipeline transportation followed by injection (generally, the temperature at the end of the pipeline is close to the ground temperature, and the compressor needs to be re-pressurized to reach the required reinjection pressure before reinjection, and the reinjection temperature is relatively high), CO2 injected by low-temperature liquid phase can make full use of the upstream CO2 liquefaction cold energy (generally the storage temperature is around -20°C), and has the potential to achieve energy-saving injection while greatly optimizing the external cold energy input. In general, for the low-temperature liquid phase injection mode, CO2 geological storage is achieved by transporting low-temperature liquefied CO2 to the injection well site for storage, and injecting it into the reinjection well through multiple pressurization. However, it still faces problems such as vaporization of the reinjection pipeline medium, reinjection temperature control, pressure protection after suspension of transportation, and abnormal downhole reinjection pressure. The key injection process still needs to be further refined.

[0004] However, there are relatively few public cases of liquid CO2 injection, and they mainly focus on the surface process flow. There is no public detailed report on the prevention of vaporization, energy-saving injection, safety protection, dynamic injection, etc. during the reinjection process. Therefore, it is necessary to fully carry out systematic research, integrate the surface reinjection system and the wellbore reinjection system, pay attention to the temperature control of the reinjection system, the overpressure protection of the reinjection system shutdown, and the abnormal pressure of the reinjection system, so as to achieve the coordinated goal of energy-saving reinjection and safe reinjection. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a CO2 efficient storage and reinjection system and method based on liquid phase injection. Based on the basic reinjection process at the wellhead, it has the functions of pre-cooling of the pipe tank before production, supercooling control of CO2 in the primary injection pipeline, optimized emission of overpressure CO2 after the ground pipeline is stopped, active pressure replenishment of the storage tank in the later stage of pressurized reinjection, and prevention and control of potential blockages in the well.

[0006] The object of the present invention is achieved through the following technical solutions:

[0007] A CO2 efficient storage and reinjection system based on liquid phase injection, the system comprises a wellhead reinjection basic system, the wellhead reinjection basic system comprises a liquid phase CO2 storage device, the outlet of the liquid phase CO2 storage device is sequentially connected to a primary injection pipeline, a secondary injection pipeline and a tertiary injection pipeline, a storage device outlet shut-off valve is arranged between the liquid phase CO2 storage device and the primary injection pipeline, a primary shielded pump is arranged between the primary injection pipeline and the secondary injection pipeline, a secondary booster pump and a tertiary injection pipeline starting point shut-off valve are arranged between the secondary injection pipeline and the tertiary injection pipeline, a tertiary injection pipeline end point shut-off valve is arranged at the end of the tertiary injection pipeline and is connected to a reinjection wellhead, the reinjection wellhead is connected to a reinjection wellbore, and the system further comprises:

[0008] A tube tank precooling system, the tube tank precooling system comprising a precooling regulating device arranged at the inlet of the liquid phase CO2 storage device and a precooling venting shutoff valve arranged at the end of the tertiary injection pipeline;

[0009] A primary injection pipeline subcooling system, the primary injection pipeline subcooling system comprising a subcooling heat exchange device disposed on the primary injection pipeline and the secondary injection pipeline, the subcooling heat exchange device being used to perform subcooling heat exchange on the medium in the primary injection pipeline;

[0010] A pipeline overpressure bypass pressure relief system, the pipeline overpressure bypass pressure relief system comprising an overpressure protection device arranged at the end of the three-stage injection pipeline;

[0011] A pressurized medium reflux pressure replenishing system, which is arranged between the outlet of the primary shielded pump and the liquid phase CO2 storage device, and is used to introduce reflux medium into the liquid phase CO2 storage device;

[0012] A downhole unblocking injection system, the downhole unblocking injection system comprising an unblocking pipeline arranged upstream of the reinjection wellhead;

[0013] A data monitoring system, the data monitoring system includes a storage device pressure monitoring device and a storage device temperature monitoring device arranged on the liquid phase CO2 storage device, a primary injection pipeline temperature monitoring device arranged on the primary injection pipeline, a secondary injection pipeline pressure monitoring device arranged on the secondary injection pipeline, a subcooling system temperature monitoring device arranged on the primary injection pipeline subcooling system, and a reflux flow monitoring device arranged on the pressurized medium reflux pressure supplement system.

[0014] Furthermore, the precooling regulating device includes an air bath type heat exchanger, the air bath type heat exchanger input port is provided with a precooling regulating valve, the air bath type heat exchanger output port is provided with a precooling shut-off valve and is connected to the liquid phase CO2 storage device.

[0015] Furthermore, the supercooling heat exchange equipment includes a heat exchanger arranged in the first-level injection pipe, the heat exchanger is connected to the second-level injection pipe through the heat exchange pipe, and a liquid intake regulating valve and a liquid intake regulating valve temperature monitoring device are also provided at the place where the heat exchange pipe enters the second-level injection pipe.

[0016] Furthermore, the overpressure protection device includes a bypass pressure relief pipeline, which is provided with a bypass shut-off valve and a bypass thermal safety valve, and the inlet end of the bypass shut-off valve is located at the inlet side of the shut-off valve at the end point of the tertiary injection pipeline.

[0017] Furthermore, the outlet end of the bypass thermal safety valve is located at the outlet side of the shut-off valve at the end of the tertiary injection pipeline, and the overpressure medium is introduced into the reinjection wellbore.

[0018] Furthermore, the overpressure protection device also includes a venting thermal safety valve and a wellhead venting riser, one end of the venting thermal safety valve is connected to the end of the three-stage injection pipeline, and the other end is connected to the wellhead venting riser.

[0019] Furthermore, the pressurized medium reflux pressure replenishing system includes a reflux pipeline connecting the outlet of the first-stage shielded pump and the liquid CO2 storage device, and the reflux pipeline is also provided with a reflux regulating valve and a reflux flow monitoring device.

[0020] Furthermore, the unblocking pipeline is provided with a reinjection shutoff valve, and the end of the unblocking pipeline is provided with a movable reinjection device.

[0021] On the other hand, the present invention also provides a CO2 efficient storage and reinjection method based on liquid phase injection, the method is implemented based on any of the aforementioned reinjection systems, and the method comprises:

[0022] Before the system is put into operation, the tube and tank precooling system is used to perform system tube and tank precooling operations;

[0023] When liquid CO2 is reinjected, the liquid CO2 in the liquid CO2 storage device is injected into the reinjection wellhead through the primary injection pipeline, the primary shielded pump, the secondary injection pipeline, the secondary booster pump and the tertiary injection pipeline. During the reinjection process, when the pressure change fluctuation of the secondary injection pipeline exceeds the preset fluctuation amplitude and / or the vibration amplitude of the primary shielded pump exceeds the preset amplitude, a portion of the pressurized liquid CO2 is adjusted to normal pressure through the supercooling heat exchange device, and the medium of the primary injection pipeline is supercooled by the low temperature caused by the pressure reduction;

[0024] After the reinjection system stops transporting, close the shut-off valve at the outlet of the storage device, the shut-off valve at the starting point of the three-stage injection pipeline, and the shut-off valve at the end of the three-stage injection pipeline, open the pipeline of the pressurized medium reflux pressure replenishment system to connect the liquid phase CO2 storage device, the first-stage injection pipeline, and the second-stage injection pipeline, and open the pipeline of the pipeline overpressure bypass pressure relief system;

[0025] After the pressure of the storage device monitoring device is lower than the preset threshold, the pressurized medium reflux pressure replenishment system is turned on to reduce the pressure and vaporize part of the liquefied CO2 reinjection amount and then lead it back to the liquid phase CO2 storage device;

[0026] When the wellhead reinjection pressure continues to increase during the reinjection process, the unblocking agent is injected through the downhole unblocking injection system, and the injection is stopped when the wellhead reinjection pressure returns to normal.

[0027] Furthermore, the blocking-removing agent includes ethylene glycol.

[0028] The beneficial effects of the present invention are:

[0029] (1) The present invention aims at the potential key problems of liquid CO2 injection, optimizes and improves the conventional injection process from multiple angles, such as pre-cooling before production, supercooling control of the first-level injection pipeline, bypass pressure relief of pipeline overpressure, reflux pressure replenishment of pressurized medium, and prevention and control of downhole blockage, so as to ensure that the system operates at a low temperature and improve the reinjection efficiency; ensure that the medium entering the pump is not vaporized, and improve the operating efficiency and safety; make full use of the receiving capacity of the wellbore and downhole for overpressure medium, and avoid direct discharge of low-temperature medium after overpressure caused by suspension of transportation; when the medium pressure of the liquid CO2 storage tank is low, the reflux medium is actively introduced to replenish the pressure of the liquid CO2 storage tank to increase the inlet pressure of the first-level shielded pump; and provide a wellhead agent injection function to address potential downhole blockage problems.

[0030] (2) The present invention controls the reinjection flow temperature of the liquid CO2 medium, optimizes the density of the injection medium, makes full use of the influence of the hydrostatic pressure of the wellbore, and reduces the surface reinjection pressure; by setting a liquid intake regulating valve, the low temperature is obtained after the pressure of the pressurized CO2 is adjusted, and the medium in the first-level injection pipeline is supercooled, avoiding the need for an additional refrigerant circulation system, and also ensuring the long-term stable operation of the boosting equipment; by setting a bypass pressure relief system, the potential direct discharge of CO2 after the injection pipeline is shut down is minimized to ensure the safety of the pipeline system; by using a reflux pressure replenishment system, the pressure in the liquid CO2 storage tank can be effectively guaranteed, the inlet pressure of the first-level shielded pump can be stabilized, and the operating energy consumption can be reduced; by setting an underground unblocking injection system, the underground reservoir blockage problem can be quickly dealt with, shortening the time to resume production. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of a CO2 efficient storage and reinjection system based on liquid phase injection provided in an embodiment of the present invention.

[0032] Figure numerals: 1-liquid CO2 storage tank, 2-storage tank pressure transmitter, 3-storage tank temperature transmitter, 4-storage tank inlet shut-off valve, 5-storage tank outlet shut-off valve, 6-first-level injection pipeline, 7-first-level shielded pump, 8-second-level injection pipeline, 9-second-level booster pump, 10-third-level injection pipeline starting point shut-off valve, 11-third-level injection pipeline, 12-third-level injection pipeline end point shut-off valve, 13-reinjection wellhead, 14-reinjection wellbore, 15-first-level injection pipeline temperature transmitter, 16-second-level injection pipeline pressure transmitter, 17-storage tank Safety valve, 18-tank area vent riser, 21-precooling regulating valve, 22-air bath heat exchanger, 23-precooling shut-off valve, 24-precooling vent shut-off valve, 31-liquid extraction regulating valve, 32-heat exchange pipeline, 33-heat exchanger, 34-temperature transmitter after regulating valve, 41-bypass shut-off valve, 42-bypass thermal safety valve, 43-venting thermal safety valve, 44-wellhead vent riser, 51-reflux regulating valve, 52-reflux pipeline, 53-reflux flow transmitter, 61-movable reinjection device, 62-reinjection shut-off valve. DETAILED DESCRIPTION

[0033] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0034] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making any creative work shall fall within the scope of protection of the present invention.

[0035] At present, there are relatively few public cases of liquid CO2 injection, and they mainly focus on the surface process flow. There is no public detailed report on the prevention of vaporization, energy-saving injection, safety protection, dynamic injection, etc. during the reinjection process. Therefore, it is necessary to fully carry out systematic research, integrate the surface reinjection system and the wellbore reinjection system, pay attention to the temperature control of the reinjection system, the overpressure protection of the reinjection system shutdown, and the abnormal pressure of the reinjection system, so as to achieve the coordinated goal of energy-saving reinjection and safe reinjection.

[0036] In order to solve the above technical problems, the following embodiments of a CO2 efficient storage and reinjection system and method based on liquid phase injection are proposed in the present invention.

[0037] Reference Figure 1 ,like Figure 1 Shown is a schematic diagram of a CO2 efficient storage and reinjection system based on liquid phase injection provided in this embodiment.

[0038] Specifically, the wellhead reinjection basic system includes a liquid CO2 storage tank 1 arranged near the reinjection wellhead, a tank pressure transmitter 2, a tank temperature transmitter 3, a tank inlet shut-off valve 4, a tank outlet shut-off valve 5, a first-level injection pipeline 6, a first-level shielded pump 7, a second-level injection pipeline 8, a second-level booster pump 9, a third-level injection pipeline starting point shut-off valve 10, a third-level injection pipeline 11, a third-level injection pipeline end point shut-off valve 12, a reinjection wellhead 13, a reinjection wellbore 14, a first-level injection pipeline temperature transmitter 15, a second-level injection pipeline pressure transmitter 16, a tank safety valve 17, a tank area venting riser 18, etc., which are used to provide basic functions such as liquid CO2 storage, pressurization and reinjection, so as to serve as the basic process of the CO2 efficient storage and reinjection system based on liquid phase injection in this embodiment.

[0039] It should be noted that in this embodiment, the first-level injection pipeline 6, the first-level shielded pump 7, the second-level injection pipeline 8, the second-level booster pump 9, the third-level injection pipeline 11, etc. are insulated to fully maintain the low temperature of the liquid CO2, increase the medium density injected into the wellbore, and reduce the wellhead reinjection pressure.

[0040] The pipe tank precooling system includes a precooling regulating valve 21, an air bath heat exchanger 22, a precooling shut-off valve 23, and a precooling venting shut-off valve 24 arranged at the end of the tertiary injection pipeline 11. It is used to introduce liquefied CO2 as a replacement and precooling medium before the reinjection system is put into production or restarted, so as to precool the ground storage tanks, pipelines, pipe fittings, etc., so as to avoid boiling or vaporization of liquid CO2 due to excessive temperature of the pipe tank body during normal injection operation.

[0041] Specifically, the precooling regulating valve 21 is arranged at the inlet of the liquid CO2 storage tank 1, and is preferably an electric regulating valve made of stainless steel, which is used to adjust the liquid CO2 to normal pressure to obtain a lower precooling temperature; the air bath heat exchanger 22 is arranged downstream of the precooling regulating valve 21, made of stainless steel, and is a movable module, which is used to perform air bath heat exchange on the low-temperature CO2 (as low as -80°C) obtained by the precooling regulating valve 21 to obtain CO2 with a temperature range of -35°C to -40°C, which is used for low-temperature purging and precooling of the downstream pipe tank system; the precooling shut-off valve 23 is a manual ball valve made of low-temperature carbon steel, which is used to cut off or connect the pipe tank precooling system; the precooling venting shut-off valve 24 is a manual shut-off valve made of low-temperature carbon steel, which is used to discharge the low-temperature CO2 introduced from the upstream to the venting riser.

[0042] The first-level injection pipeline supercooling system is arranged on the second-level injection pipeline 8, including a liquid intake regulating valve 31, a heat exchange pipeline 32, a heat exchanger 33, a temperature transmitter 34 after the regulating valve, etc., which is used to supercool the medium in the first-level injection pipeline 6 when gas blockage occurs in the first-level shielded pump 7 and the outlet pressure is abnormal, and actively reduce the temperature of the liquid phase CO2 in the first-level injection pipeline 6 to avoid the formation of gas-liquid two-phase before entering the first-level shielded pump 7 and when passing through the first-level shielded pump 7.

[0043] Specifically, the liquid taking regulating valve 31 is arranged on the secondary injection pipeline 8, and is an electric regulating valve made of stainless steel. It is used to take the liquid phase CO2 after the first stage of pressurization from the secondary injection pipeline 8, obtain low-temperature gas through throttling, and supply it to the heat exchanger 33 to reduce the medium temperature of the primary injection pipeline 6 and achieve medium supercooling; the heat exchange pipeline 32 connects the liquid taking regulating valve 31 and the heat exchanger 33, and is made of stainless steel; the heat exchanger 33 is preferably a multi-tube heat exchanger, which is used for supercooling heat exchange between the low-temperature CO2 obtained by the liquid taking regulating valve 31 and the medium of the primary injection pipeline 6, and the temperature after heat exchange is controlled to be 5°C lower than the bubble point temperature corresponding to the CO2 medium under the operating pressure at this time.

[0044] The pipeline overpressure bypass pressure relief system is arranged at the end of the tertiary injection pipeline 11, including a bypass shut-off valve 41, a bypass thermal safety valve 42, a venting thermal safety valve 43, a wellhead venting riser 44, etc., which is used to perform overpressure protection on the tertiary injection pipeline 11 separated by the shut-off valve 10 at the starting point of the tertiary injection pipeline and the shut-off valve 12 at the end point of the tertiary injection pipeline after the injection is stopped, and make full use of the pressure receiving capacity of the downhole wellbore and the reservoir, preferably introduce the overpressure medium caused by the increase in ambient temperature in the ground closed pipeline into the wellbore to avoid direct discharge, and at the same time provide a second layer of pressure protection for the overpressure medium of the ground closed pipeline to be discharged to the wellhead venting riser.

[0045] Specifically, the bypass shut-off valve 41 is arranged at the end point of the tertiary injection pipeline to bypass the shut-off valve 12, is a manual shut-off valve, made of low-temperature carbon steel, normally closed, and opened after the reinjection system is shut down; the bypass thermal safety valve 42 is a thermal safety valve, which is opened after the internal medium pressure of the medium in the tertiary injection pipeline 11 increases due to the temperature rise of the environment and exceeds the set value, and discharges the overpressure medium into the downstream wellhead and wellbore to prevent the overpressure medium from directly entering the venting system, and its set pressure is 95% of the design pressure of the tertiary injection pipeline 11; the venting thermal safety valve 43 is a thermal safety valve, which is arranged on the tertiary injection pipeline 11, and is the second level of protection for thermal overpressure. When the bypass thermal safety valve 42 cannot effectively reduce the thermal overpressure of the tertiary injection pipeline 11, it is activated, and its set pressure is 105% of the design pressure of the tertiary injection pipeline 11; the wellhead venting riser 44 is arranged at the wellhead, which is used to safely discharge the thermal overpressure medium and simultaneously support the release of the precooling medium of the pipe tank precooling system.

[0046] The pressurized medium reflux pressure-compensating system is arranged at the outlet of the first-stage shielded pump 7, including a reflux regulating valve 51, a reflux pipe 52, a reflux flow transmitter 53, etc. It is used to compensating the liquid CO2 storage tank 1 by actively introducing reflux medium when the medium pressure in the liquid CO2 storage tank 1 is low, so as to increase the inlet pressure of the first-stage shielded pump 7.

[0047] Specifically, the reflux regulating valve 51 is arranged at the outlet of the first-stage shielded pump 7. It is an electric regulating valve made of low-temperature carbon steel. It is used to take part of the CO2 from the second-stage injection pipeline 8 for throttling and vaporization, and reflux it to the gas phase area of ​​the liquid CO2 storage tank 1 to replenish the tank pressure; the reflux pipeline 52 connects the reflux regulating valve 51 and the liquid CO2 storage tank 1, and is made of low-temperature carbon steel. It is not insulated, so as to make full use of the ambient temperature to slightly heat the medium in the pipeline and inject it into the liquid CO2 storage tank 1; the reflux flow transmitter 53 is used to monitor the flow of reflux CO2.

[0048] The downhole de-blocking injection system is arranged upstream of the reinjection wellhead 13, and includes a movable reinjection device 61, a reinjection shut-off valve 62, etc., which is used to inject de-blocking agents to alleviate the potential blockage problem of solid phase precipitation in the downhole reservoir caused by CO2 injection, and alleviate the problem of long-term excessive reinjection pressure caused by downhole reservoir blockage.

[0049] Specifically, the movable reinjection device 61 is preferably a movable skid-mounted equipment with ethylene glycol (MEG) storage, metering and pressurization, which is used to provide ethylene glycol (MEG) reinjection function and alleviate potential reservoir blockage problems that may exist underground due to CO2 reinjection; the reinjection shut-off valve 62 is a manual ball valve, which is used to connect or isolate the movable reinjection device 61.

[0050] In this embodiment, the pipe tank precooling system is arranged on the ground storage tank, including a regulating valve, a vaporizer, etc., which is used for precooling the ground pipe tank system before it is put into production or put into use; the first-level injection pipeline supercooling system is installed on the first-level injection pipeline connecting the storage tank outlet and the first-level shielded pump, including a regulating valve after the shielded pump, a low-temperature pipeline, a heat exchanger, a venting pipeline, etc., which is used to supercool the first-level injection pipeline in the event of vibration of the first-level shielded pump, abnormal outlet pressure, etc., to ensure the boosting performance of the first-level shielded pump; the pipeline overpressure bypass pressure relief system is arranged at the end of the tertiary injection pipeline, including a bypass shut-off valve, a bypass overpressure relief valve, an overpressure venting valve, etc., which is used to relieve the overpressure caused by the environment after the tertiary injection pipeline is shut down. The rising ambient temperature causes the medium in the pipeline to expand and overpressure for protection. The overpressure medium is preferentially introduced into the wellbore through the bypass, and the secondary protection function of introducing the overpressure medium in the pipeline into the venting system is provided; the pressurized medium reflux pressure supplement system is set at the downstream of the first-level shielded pump, including bypass pipeline, pressure regulating valve, reflux pipeline, etc., which is used to introduce vaporized CO2 through reflux when the tank liquid level is low, increase the tank pressure, and supplement the suction pressure of the first-level shielded pump; the underground unblocking injection system is set at the end of the third-level injection pipeline, including a reserved injection shut-off valve and a movable injection skid, which is used to inject unblocking agents from the wellhead when potential flow channel blockage caused by CO2 injection occurs underground. In this way, efficient and safe liquid-phase CO2 reinjection is achieved.

[0051] The working principle of the CO2 efficient storage and reinjection system based on liquid phase injection in this embodiment is as follows:

[0052] The system is based on the basic physical properties of CO2, the laws of gasification and liquefaction, the basic process of wellhead reinjection, the basic influencing factors of wellhead reinjection pressure, etc., and aims at the engineering needs of liquid CO2 wellhead reinjection. From the perspective of safe reinjection and efficient reinjection, it has set up a pipe tank precooling system, a first-level injection pipeline supercooling system, a pipeline overpressure bypass pressure relief system, a pressurized medium return pressure replenishment system and an underground unblocking injection system, etc., so as to fully take advantage of the basic wellhead reinjection process to form a system with functions such as pipe tank precooling before production, CO2 supercooling control in the first-level injection pipeline, optimized emission of overpressure CO2 after the ground pipeline is shut down, active pressure replenishment of the storage tank in the later stage of pressurized reinjection, and prevention and control of potential blockages in the well. Among them, the pipe tank precooling system is set on the ground storage tank, including regulating valves, vaporizers, etc., which are used for precooling the ground pipe tank system before it is put into production or put into use; the first-level injection pipeline supercooling system is installed on the first-level injection pipeline connecting the storage tank outlet and the first-level shielded pump, including the shielded pump rear regulating valve, low-temperature pipeline, heat exchanger, venting pipeline, etc., which is used to supercool the first-level injection pipeline in the event of vibration of the first-level shielded pump, abnormal outlet pressure, etc., to ensure the pressurization performance of the first-level shielded pump; the pipeline overpressure bypass pressure relief system is set at the end of the tertiary injection pipeline, including bypass shut-off valve, bypass overpressure relief valve, overpressure vent valve, etc., which is used to relieve the overpressure caused by the environment after the tertiary injection pipeline is shut down. The temperature rise causes the medium in the pipeline to expand and overpressure for protection. The overpressure medium is preferentially introduced into the wellbore through the bypass, and a secondary protection function is provided for the overpressure medium in the pipeline to be introduced into the venting system as a backup. The pressurized medium reflux pressure supplement system is set at the downstream of the first-level shielded pump, including bypass pipeline, pressure regulating valve, reflux pipeline, etc., which is used to introduce vaporized CO2 through reflux when the tank liquid level is low, increase the tank pressure, and supplement the suction pressure of the first-level shielded pump. The underground unblocking injection system is set at the end of the third-level injection pipeline, including a reserved injection shut-off valve and a movable injection skid, which is used to inject unblocking agents from the wellhead when potential flow channel blockage caused by CO2 injection occurs underground. In this way, efficient and safe liquid-phase CO2 reinjection is achieved.

[0053] During normal reinjection, liquid CO2 transported by a tank truck is injected into the liquid CO2 storage tank 1, and then a stable boosting pressure is provided by the first-level shielded pump 7, and reinjection is performed after the pressure is increased to the wellhead reinjection pressure by the second-level booster pump 9.

[0054] In order to increase the density of the injected medium, this embodiment proposes to insulate the first-level injection pipeline 6, the first-level shielded pump 7, the second-level injection pipeline 8, the second-level booster pump 9, the third-level injection pipeline 11, etc., so as to fully maintain the low temperature of the liquid CO2, increase the density of the medium injected into the wellbore, and reduce the wellhead reinjection pressure.

[0055] Since the initial temperature of the tube-tank system is relatively high (not pre-cooled) and the pressure is relatively low (not pressurized), the liquid CO2 introduced from the outside (temperature at -25°C to -20°C, pressure at about 2.0 MPa) may vaporize violently. Therefore, this embodiment proposes to set up a tube-tank pre-cooling system to obtain low-temperature gaseous CO2 through throttling and heat exchange, and to pre-cool and pressurize the tube-tank system.

[0056] The first-stage shielded pump 7 may be affected by the vaporization of the inlet medium and the vaporization of the medium in the pump, causing the first-stage shielded pump 7 to vibrate and the outlet air blockage. Therefore, the present embodiment provides a first-stage injection pipeline supercooling system to perform supercooling heat exchange on the medium in the first-stage injection pipeline 6, actively reduce the temperature of the liquid CO2 in the first-stage injection pipeline 6, and avoid the formation of gas-liquid two-phase before entering the first-stage shielded pump 7 and when passing through the first-stage shielded pump 7.

[0057] Since the injection system uses relatively low-temperature CO2, after the system stops transmitting, the pipeline system will be affected by the external environment, and the problem of increased pressure of the medium in the pipe caused by the increased temperature will occur. For this reason, the present embodiment provides a pipeline overpressure bypass pressure relief system for overpressure protection of the third-level injection pipeline 11 separated by the third-level injection pipeline starting point shut-off valve 10 and the third-level injection pipeline end point shut-off valve 12 after the injection stops, and fully utilizes the pressure receiving capacity of the downhole wellbore and the reservoir, preferably directing the overpressure medium caused by the increase in ambient temperature in the ground closed pipeline into the wellbore to avoid direct discharge, and at the same time providing a second layer of pressure protection for the overpressure medium in the ground closed pipeline to be discharged to the wellhead venting riser.

[0058] After the liquid CO2 storage tank 1 continuously outputs CO2, the medium in the tank gradually decreases, causing the pressure in the tank to decrease, increasing the boost load of the first-stage shielded pump 7. To this end, the present embodiment is provided with a boost medium reflux pressure replenishment system, which is used to actively introduce reflux medium to replenish the pressure of the liquid CO2 storage tank 1 when the medium pressure in the liquid CO2 storage tank 1 is low, so as to increase the inlet pressure of the first-stage shielded pump 7. By partially throttling, exchanging heat, and reinjecting the pressurized liquid CO2 into the liquid CO2 storage tank, the gas phase temperature and gas phase volume of the liquid CO2 storage tank are increased, which has the effect of actively increasing the operating pressure of the liquid CO2 storage tank.

[0059] Potential CO2 injection may cause solid phase precipitation and blockage problems in downhole reservoirs, mainly because the dehydrated CO2 may absorb moisture from the saline layer downhole, causing salt precipitation and blocking the flow path. For this reason, this embodiment provides a downhole unblocking injection system to alleviate the problem of long-term excessive re-injection pressure caused by blockage of the downhole reservoir by injecting unblocking agents (preferably MEG).

[0060] This embodiment implements a CO2 efficient storage and reinjection method based on liquid phase injection according to the aforementioned system, including the following contents:

[0061] Step 1: After the overall drying and replacement of the pipe and tank system, the system pipe and tank precooling operation is required before the system is put into operation, using the low temperature after the liquid CO2 vaporizes to provide cooling capacity, and at the same time complete the replacement of the pipe and tank system. Specifically, close the tank inlet shut-off valve 4 and the end shut-off valve 12 of the three-stage injection pipeline, open the tank outlet shut-off valve 5, the three-stage injection pipeline starting point shut-off valve 10, and the precooling venting shut-off valve 24; input liquid CO2 at -20℃ to -25℃ upstream of the precooling regulating valve 21, open the precooling regulating valve 21, the air bath heat exchanger 22, and the precooling shut-off valve 23, and adjust the temperature after the air bath heat exchanger 22 to -35℃ to -40℃, and continuously provide low-temperature CO2 gas to the storage tank and downstream pipelines. , temperature monitoring is carried out through temperature transmitters at multiple points in the system. When the temperature of the temperature transmitters at various points in the system is lower than -25°C for 10 minutes, the pre-cooling vent shut-off valve 24 is closed, the CO2 input to the storage tank is maintained, and the system is gradually pressure-filled until the pressure of the liquid CO2 storage tank 1, the first-level injection pipeline 6, the second-level injection pipeline 8 and the third-level injection pipeline 11 is not lower than 1.5MPa. Stop filling to provide sufficient back pressure for the subsequent reinjection operation to avoid causing too low a filling throttling temperature.

[0062] Step 2: When liquid CO2 is reinjected, the liquid CO2 in the liquid CO2 storage tank 1 is injected into the wellhead through the primary injection pipeline 6, the primary shielded pump 7, the secondary injection pipeline 8, the secondary booster pump 9, the tertiary injection pipeline 11, etc. During this process, continue to pay attention to the pressure changes of the secondary injection pipeline pressure transmitter 16 and the vibration of the primary shielded pump 7. When there is a large pressure fluctuation or the outlet pressure or the primary shielded pump vibrates significantly, it indicates that the medium in the primary injection pipeline 6 is affected by the flow temperature rise and vaporizes, or the primary shielded pump 7 affects the fluid temperature rise and vaporizes. In this case, open the liquid intake regulating valve 31, adjust the pressure of a part of the pressurized liquid CO2 to normal pressure, and use the low temperature caused by the pressure reduction to supercool the medium in the primary injection pipeline 6 in the heat exchanger 33, and control the temperature after heat exchange to be 5°C lower than the bubble point temperature corresponding to the CO2 medium at the operating pressure at this time. The low-temperature CO2 used for heat exchange is discharged into the venting riser 18 in the storage tank area.

[0063] Step 3: After the reinjection system stops, close the tank outlet shutoff valve 5, the tertiary injection pipeline start point shutoff valve 10, and the tertiary injection pipeline end point shutoff valve 12 to isolate the tank from the pump system, the ground injection pipeline system (tertiary injection pipeline 11) and the wellhead. Actively open the reflux regulating valve 51 to connect the liquid CO2 storage tank 1, the primary injection pipeline 6, and the secondary injection pipeline 8 to prevent the pipeline from being closed and thermally expanded due to heat input from the external environment. Open the bypass shutoff valve 41. When the internal medium of the tertiary injection pipeline 11 is affected by the external environment and the temperature rises, the overpressure medium is preferentially introduced into the wellhead and wellbore through the bypass thermal safety valve 42 (because the bottom hole pressure is basically stable, and the pressurization amplitude of the medium in the wellbore due to thermal expansion may be smaller than that of the ground pipeline) to avoid direct discharge; when the medium pressure in the tertiary injection pipeline 11 continues to rise, the second-level pressure protection is performed by opening the venting thermal safety valve 43.

[0064] Step 4: After the liquid level of the liquid CO2 storage tank 1 continues to decrease, the pressure inside the tank may continue to decrease, causing the inlet pressure of the primary shielded pump 7 to be too low, resulting in increased energy consumption. Therefore, it is preferred that when the pressure of the tank pressure transmitter 2 is lower than 1.2MPag, the reflux regulating valve 51 is opened to reduce the pressure and vaporize 5% of the liquefied CO2 reinjection amount and then lead it back to the liquid CO2 storage tank 1. Since the reflux pipe 52 is not insulated, the medium flowing back into the liquid CO2 storage tank 1 must be in the gas phase, which can significantly increase the internal pressure of the liquid CO2 storage tank 1.

[0065] Step 5: During the reinjection process, if the wellhead reinjection pressure continues to increase significantly, it is possible that the underground storage is blocked by salt due to the absorption of water in the brine by CO2. To this end, the movable reinjection device 61 can be connected to the reinjection shutoff valve 62, and the injection medium is preferably ethylene glycol, which is used to reduce the water absorption of the injected CO2 and improve the water decomposition of the water-containing CO2 underground. When the wellhead reinjection pressure returns to normal, stop the injection.

[0066] Therefore, through the control of multiple key issues, efficient and safe reinjection of liquid CO2 can be achieved.

[0067] Compared with the prior art, the positive effects of this embodiment are based on the basic physical properties of CO2, the laws of gasification and liquefaction, the basic process of wellhead reinjection, the basic influencing factors of wellhead reinjection pressure, etc., and aiming at the engineering needs of liquid CO2 wellhead reinjection, from the perspective of safe reinjection and efficient reinjection, a pipe tank precooling system, a first-level injection pipeline supercooling system, a pipeline overpressure bypass pressure relief system, a pressurized medium return pressure replenishing system and an underground unblocking injection system are respectively set up, so as to fully form an efficient storage and injection system with the functions of pipe tank precooling before production, CO2 supercooling control in the first-level injection pipeline, optimized emission of overpressure CO2 after the ground pipeline is stopped, active pressure replenishment of the storage tank in the later stage of pressurized reinjection, and prevention and control of potential blockages in the well based on the basic wellhead reinjection process.

[0068] Specifically manifested as:

[0069] (1) Aiming at the potential key problems of liquid CO2 injection, the conventional injection process is optimized and improved from multiple angles, such as pre-cooling before production, overcooling control of the first-stage injection pipeline, bypass pressure relief of pipeline overpressure, reflux pressure replenishment of pressurized medium, and prevention and control of downhole blockage, to ensure that the system operates at a low temperature and improve the reinjection efficiency; ensure that the medium entering the pump does not vaporize, and improve the operating efficiency and safety; make full use of the wellbore and downhole receiving capacity of overpressure medium to avoid direct discharge of low-temperature medium after overpressure caused by suspension of transportation; when the medium pressure of the liquid CO2 storage tank 1 is low, the reflux medium is actively introduced to replenish the pressure of the liquid CO2 storage tank 1 to increase the inlet pressure of the first-stage shielded pump 7; and provide a wellhead agent injection function to address potential downhole blockage problems.

[0070] (2) By controlling the reinjection flow temperature of the liquid CO2 medium, optimizing the density of the injected medium, and making full use of the influence of the hydrostatic pressure of the wellbore, the surface reinjection pressure is reduced; by setting the liquid intake regulating valve 31, the low temperature is obtained after the pressure of the pressurized CO2 is adjusted, and the medium in the first-level injection pipeline is supercooled, avoiding the need for an additional refrigerant circulation system, and also ensuring the long-term stable operation of the boosting equipment; by setting a bypass pressure relief system, the potential direct discharge of CO2 after the injection pipeline is shut down is minimized to ensure the safety of the pipeline system; by using the reflux pressure replenishment system, the pressure in the liquid CO2 storage tank can be effectively guaranteed, the inlet pressure of the first-level shielded pump 7 can be stabilized, and the operating energy consumption can be reduced; by setting an underground unblocking injection system, the underground reservoir blockage problem can be quickly responded to, shortening the time for re-commissioning.

[0071] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A CO2 efficient storage and reinjection system based on liquid phase injection, the system comprising a wellhead reinjection basic system, the wellhead reinjection basic system comprising a liquid phase CO2 storage device, the outlet of the liquid phase CO2 storage device is sequentially connected to a primary injection pipeline, a secondary injection pipeline and a tertiary injection pipeline, a storage device outlet shut-off valve is provided between the liquid phase CO2 storage device and the primary injection pipeline, a primary shielded pump is provided between the primary injection pipeline and the secondary injection pipeline, a secondary booster pump and a tertiary injection pipeline starting point shut-off valve are provided between the secondary injection pipeline and the tertiary injection pipeline, a tertiary injection pipeline end point shut-off valve is provided at the end of the tertiary injection pipeline and is connected to the reinjection wellhead, the reinjection wellhead is connected to the reinjection wellbore, characterized in that: The system further comprises: A tube tank precooling system, the tube tank precooling system comprising a precooling regulating device arranged at the inlet of the liquid phase CO2 storage device and a precooling venting shutoff valve arranged at the end of the tertiary injection pipeline; A primary injection pipeline subcooling system, the primary injection pipeline subcooling system comprising a subcooling heat exchange device disposed on the primary injection pipeline and the secondary injection pipeline, the subcooling heat exchange device being used to perform subcooling heat exchange on the medium in the primary injection pipeline; A pipeline overpressure bypass pressure relief system, the pipeline overpressure bypass pressure relief system comprising an overpressure protection device arranged at the end of the three-stage injection pipeline; A pressurized medium reflux pressure replenishing system, which is arranged between the outlet of the primary shielded pump and the liquid phase CO2 storage device, and is used to introduce reflux medium into the liquid phase CO2 storage device; A downhole unblocking injection system, the downhole unblocking injection system comprising an unblocking pipeline arranged upstream of the reinjection wellhead; A data monitoring system, the data monitoring system includes a storage device pressure monitoring device and a storage device temperature monitoring device arranged on the liquid phase CO2 storage device, a primary injection pipeline temperature monitoring device arranged on the primary injection pipeline, a secondary injection pipeline pressure monitoring device arranged on the secondary injection pipeline, a subcooling system temperature monitoring device arranged on the primary injection pipeline subcooling system, and a reflux flow monitoring device arranged on the pressurized medium reflux pressure supplement system.

2. The CO2 efficient storage and reinjection system based on liquid phase injection according to claim 1 is characterized in that: The precooling regulating device comprises an air bath type heat exchanger, the inlet of the air bath type heat exchanger is provided with a precooling regulating valve, the outlet of the air bath type heat exchanger is provided with a precooling shut-off valve and is connected to the liquid phase CO2 storage device.

3. The CO2 efficient storage and reinjection system based on liquid phase injection according to claim 1 is characterized in that: The supercooling heat exchange equipment includes a heat exchanger arranged in the primary injection pipeline, the heat exchanger is connected to the secondary injection pipeline through the heat exchange pipeline, and a liquid intake regulating valve and a liquid intake regulating valve temperature monitoring device are also provided at the place where the heat exchange pipeline enters the secondary injection pipeline.

4. The CO2 efficient storage and reinjection system based on liquid phase injection according to claim 1 is characterized in that: The overpressure protection device comprises a bypass pressure relief pipeline, which is provided with a bypass shutoff valve and a bypass thermal safety valve, and the inlet end of the bypass shutoff valve is located at the inlet side of the shutoff valve at the end point of the tertiary injection pipeline.

5. The CO2 efficient storage and reinjection system based on liquid phase injection according to claim 4 is characterized in that: The outlet end of the bypass thermal safety valve is located at the outlet side of the cut-off valve at the end of the tertiary injection pipeline, and the overpressure medium is introduced into the reinjection wellbore.

6. The CO2 efficient storage and reinjection system based on liquid phase injection according to claim 4 is characterized in that: The overpressure protection device also includes a venting thermal safety valve and a wellhead venting riser, one end of the venting thermal safety valve is connected to the end of the three-stage injection pipeline, and the other end is connected to the wellhead venting riser.

7. The CO2 efficient storage and reinjection system based on liquid phase injection according to claim 1 is characterized in that: The pressurized medium reflux pressure replenishment system comprises a reflux pipeline connecting the outlet of the first-stage shielded pump and the liquid CO2 storage device, and a reflux regulating valve and a reflux flow monitoring device are also provided on the reflux pipeline.

8. The CO2 efficient storage and reinjection system based on liquid phase injection according to claim 1 is characterized in that: The unblocking pipeline is provided with a reinjection shutoff valve, and the end of the unblocking pipeline is provided with a movable reinjection device.

9. A CO2 efficient storage and reinjection method based on liquid phase injection, characterized in that: The method is implemented based on the reinjection system according to any one of claims 1 to 8, and the method comprises: Before the system is put into operation, the tube and tank precooling system is used to perform system tube and tank precooling operations; When liquid CO2 is reinjected, the liquid CO2 in the liquid CO2 storage device is injected into the reinjection wellhead through the primary injection pipeline, the primary shielded pump, the secondary injection pipeline, the secondary booster pump and the tertiary injection pipeline. During the reinjection process, when the pressure change fluctuation of the secondary injection pipeline exceeds the preset fluctuation amplitude and / or the vibration amplitude of the primary shielded pump exceeds the preset amplitude, a portion of the pressurized liquid CO2 is adjusted to normal pressure through the supercooling heat exchange device, and the medium of the primary injection pipeline is supercooled by the low temperature caused by the pressure reduction; After the reinjection system stops transporting, close the shut-off valve at the outlet of the storage device, the shut-off valve at the starting point of the three-stage injection pipeline, and the shut-off valve at the end of the three-stage injection pipeline, open the pipeline of the pressurized medium reflux pressure replenishment system to connect the liquid phase CO2 storage device, the first-stage injection pipeline, and the second-stage injection pipeline, and open the pipeline of the pipeline overpressure bypass pressure relief system; After the pressure of the storage device monitoring device is lower than the preset threshold, the pressurized medium reflux pressure replenishment system is turned on to reduce the pressure and vaporize part of the liquefied CO2 reinjection amount and then lead it back to the liquid phase CO2 storage device; When the wellhead reinjection pressure continues to increase during the reinjection process, the unblocking agent is injected through the downhole unblocking injection system, and the injection is stopped when the wellhead reinjection pressure returns to normal.

10. The CO2 efficient storage and reinjection method based on liquid phase injection according to claim 9, characterized in that: The blocking-removing agent includes ethylene glycol.

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